The document discusses the mechanical compaction of concrete, emphasizing its importance for enhancing strength and durability by removing air voids through various vibration techniques, including immersion, surface, and form vibration. It details different types of vibrators, their effective usage, and guidelines for achieving optimal compaction. The conclusion highlights that complete compaction significantly improves concrete properties crucial for construction.

1. MECHANICAL COMPACTION
OF CONCRETE
By: Abhishek Shah

2. CONTENT . . . .
Introduction
Importance of Compaction of Concrete
Mechanical Compaction of concrete
Immersion Vibration
Case Study on Immersion vibration

3. Surface vibrator
Form vibrator
Conclusion
Acknowledgement
References

4. INTRODUCTION TO COMPACTION
OF
CONCRETE
• Compaction is the process which
expels entrapped air from freshly
placed concrete and packs the
aggregate particles together so
as to increase the density of
concrete. Fig. 1
• Compaction is actually two stage
process Fig. 2
Fig.1 Fresh Concrete Compaction
Source : Google Images

5. Fig. 2 Compaction of Fresh Concrete
Source : Google Images

6. STAGES OF COMPACTION OF
CONCRETE
• Stage 1:
with vibration, initial consolidation of the concrete can often be achieved relatively
quickly. The concrete liquefies and the surface levels, giving the impression that the
concrete is compacted
• Stage 2:
In the second stage, entrapped air is expelled. Entrapped air takes a little longer to
rise to the surface. Compaction must therefore be prolonged until this is
accomplished, ie until air bubbles no longer appear on the surface.

7. IMPORTANCE OF COMPACTION

8. • It is important to compact the concrete fully because, Air voids reduce
the strength of the concrete. For every 1% of entrapped air, the
strength falls by somewhere between 5 and 7%. This means that
concrete containing about 5% air voids due to incomplete compaction
can lose as much as one third of its strength. Figure 3
• Air voids increase concrete's permeability. That in turn reduces its
durability.
• If the concrete is not dense and impermeable, it will not be watertight.
It will be less able to withstand aggressive liquids and its exposed
surfaces will weather badly.
• Moisture and air are more likely to penetrate to the reinforcement
causing it to rust.
• Air voids impair contact between the mix and reinforcement (and,
indeed, any other embedded metals). The required bond will not be
achieved and the reinforced member will not be as strong as it should

9. • It increases significantly the ultimate strength of concrete and enhances
the bond with reinforcement.
• It also increases the abrasion resistance and general durability of the
concrete, decreases the permeability and helps to minimize its
shrinkage-and-creep characteristics.
• Proper compaction also ensures that the formwork is completely filled
i.e. there are no pockets of honeycombed material and that the required
finish is obtained on vertical surfaces
• When first placed in the form, normal concrete, excluding those with
very low or very high slumps, will contain between 5% and 20% by
volume of entrapped air. The aggregate particles, although coated with
mortar, tend to arch against one another and are prevented from
slumping or consolidating by internal friction.

11. MECHANICAL COMPACTION OF
CONCRETE
Immersion Vibration :
• In immersion vibration a mechanical
device termed as needle vibrator is broadly
used by many firms Fig. 4
• immersion vibrators consist essentially of a
tubular housing which contains a rotating
eccentric weight. The out-of-balance
rotating weight causes the casing to
vibrate Fig. 5 Fig 4. Immersion Vibrator
Source : Google Images

12. DETAIL SKETCH OF NEEDLE
VIBRATOR
Fig. 5 Immersion Vibrator
Source : Google Images

13. • The out-of-balance rotating weight causes
the casing to vibrate.
• When immersed in concrete, the concrete
itself. Depending on the diameter of the
casing or head, and on the frequency and
the amplitude of the vibration, an immersion
vibrator may have a radius of action
between 100 and 600 mm
• The effectiveness of an immersion vibrator is
dependent on its frequency and amplitude,
the latter being dependent on the size of the
head, the eccentric moment and the head
weight – the larger the head, the larger the
amplitude.
Fig. 6 Working with needle vibrator
Source : Google Images

14. RECOMMENDATION FOR USE OF
POKER VIBRATOR
Diameter
of head
(mm)
Recommended
Frequency
(HZ)
Average
Amplitude
(mm)
Radius of
Action
()
Rate of
Concreting
(cmt/hour)
20–40 150–250 0.4–0.8 75–150 1–4
30–65 140–210 0.5–1.0 125–250 2–8
50–90 130–200 0.6–1.3 175–350 6–20
75–150 120–180 0.8–1.5 300–500 11–31
125–175 90–140 1.0–2.0 400–600 19–38
Adapted from Table 5.1 ACI Committee Report: Guide for Consolidation of
Concrete 309R-05 ACI Manual of Concrete Practice 2006 Part 2.

15. FOLLOWING CARE SHOULD BE
TAKEN WHILE USING NEEDLE
VIBRATOR
• As a general rule, the radius of action of
a given vibrator not only increases with
the workability of the concrete (higher
slump), but also with the diameter of the
head
• Immersion vibrators should be inserted
vertically into concrete, as quickly as
possible, and then held stationary until
air bubbles cease to rise to the surface,
usually in about 15–20 seconds
Fig. 7 vertical position of needle
Source : Google Images

16. • The vibrator should then be slowly
withdrawn and reinserted vertically in a
fresh position adjacent to the first. These
movements should be repeated in a
regular pattern until all the concrete has
been compacted Fig. 7
• Random insertions are likely to leave
areas of the concrete uncompacted.
• One should try that minimum overlap of
this vibration circle should allowed Fig. 8
• The vibrator should not be used to cause
concrete to flow horizontally in the forms,
as this can lead to segregation
Fig. 8 Overlap of vibration radius of
vibrator
Source : CCANZ Bulletin

17. • the vibrator should not be dragged through the concrete as this
leads to inadequate compaction and increases the risk of
segregation.
• In deep sections such as walls, footings and large columns, the
concrete should be placed in layers about 300 mm thick
• The vibrator should penetrate about 150 mm into the previous layer
of fresh concrete to meld the two layers together and avoid ‘cold-
pour’ lines on the finished surface
• The vibrator should not be allowed to touch the forms as this can
cause ‘burn’ marks which will be reflected on the finished surface
• Similarly, the vibrator should not be held against the reinforcement
as this may cause its displacement.

18. • inclined forms are prone to trapping air.
To minimize this tendency, the best
technique is to place the concrete close
to, but away from the side of the form and
insert the immersion vibrator close to the
leading edge of the concrete, forcing it to
properly fill the corner Fig. 9
• Void-formers are also prone to trapping
air on their undersides if concrete is
placed from both sides and then
compacted. Concrete should be placed at
one side and, maintaining a head,
vibrated until it appears at the other side.
Fig. 9 Pouring of Concrete
Source : CCAA bulletin

19. Surface vibration:
• Surface vibrators are applied to the top
surface of concrete and act downwards
from there.
• They are very useful for compacting
slabs, industrial floors, road
pavements, and similar flat surfaces.
They also aid in leveling and finishing
the surface. Fig. 10
• There are a number of types of surface
vibrators including vibrating-roller
screeds, vibrating-beam screeds
• The most common type is the single or
double vibrating-beam screed. Or
Roller screed
Fig. 10 Typical surface vibrator
Source : Google Images

20. Beam Screed vibrator
• A vibrating-beam screed
consists of either one or two
beams, made from aluminum,
steel or timber, to which is
attached a form of vibrating unit
to allow the beams to impart
adequate vibration to the
concrete Fig. 11
• This may be a single unit,
mounted centrally, or may
consist of a series of eccentric
weights on a shaft driven from a
Fig. 11 Double Beam Screed
vibrator
Source : Google Images

21. • In general, the centrally-mounted
units have a maximum span of about
6 m, but the trussed units may span
up to 20 m.
• The intensity of vibration, and hence
the amount of compaction achieved,
decreases with depth because
surface vibrators act from the top
down.
• Therefore, the slab thickness for
which compaction by surface
vibrators is effective will vary (from
100 to 200 mm) depending on the
Depth of
compaction
decreases
in vicinity of
edge forms
Depth of
compaction
(maximum
200 mm)
Immersion
vibrators
needed to
supplement
compaction
here
Surface vibratorEdge
Form
Fig. 12 Effect of Surface Vibrator
Source : Google Images

22. • With centrally-mounted vibration units, the degree of
compaction achieved may vary across the width of the beam
Fig. 12
• It is generally desirable, therefore, to supplement vibrating-
beam compaction by using immersion vibrators alongside edge
forms.
• The effectiveness of vibration, and hence degree of
compaction, increases with an increase in the beam weight, the
amplitude and the frequency,
• As the forward speed of beam increases compaction decreases
and vise versa
• Speed of screed should be limited to between 0.5 and 1.0
m/min. for getting batter output
• The lower speed should be used for thicker slabs and where
reinforcement is close to the top face

23. Roller Screed vibrator :
• Roller screed vibrator are same of
that beam screed vibrators Fig. 13
• In this type of vibrator beam is
replaced by long cylindrical roller
• Here roller is given vibration through
internal rotating imbalanced weight
• Vibration is occurred throughout the
cross section is same
Fig. 13 Roller screed vibrator
Source : Google Images

24. Plate Vibrator :
• Plate vibrator are generally used in
laboratories Fig. 14
• It is generally used for compaction of
practical specification made in lab
• It is not preferred on large scale of
concreting done on big sites
• Vibrating table techniques are usually
restricted to recasting operations
• Also reflection of the pressure waves
against the concrete surface will influence
the amplitude distribution
• Table vibrators can give less consistent
results even with careful operation.
Fig. 14 Plate vibrator
Source : Google Images

25. Form vibration:
• In form vibration a mechanical
vibrating device is used and it is
attached with the form work Fig.15
,Fig. 16
• Form vibrators are useful with
complicated members or where the
reinforcement is highly congested
• They are clamped to the outside of the
formwork and vibrate it thus
compacting the concrete
• in this type of vibration first vibration is
transferred to the form work and then it
is transferred to the concrete
Fig. 15 Form vibrator
Source : Google Images

26. • Due to above reason it consumes more
power then the ordinary vibrators
• The formwork will need to be
specifically designed to resist the forces
imposed on it.
• All joint of the form work should
specially design to withstand against
the rapid shocking movement
Fig. 16 Form vibrator
Source : Google Images

27. CONCLUSION
• In today’s rapid growing world Concrete is most essential
material for construction.
• But the concrete properties like strength, durability,
serviceability are the problem.
• But with complete compaction of concrete one can improve
concrete property like strength, durability, serviceability with
great extent.

28. REFERENCE
• Concrete technology by M. S. Shetty
• www.google.com
• www.concretetools.co.nz
• www.concrete.net.au
• www.vibco.com